The mechanism of action of zinc thiophosphates as extreme pressure agents

Measurements of the kinetics of interaction between a typical zinc dialkyl dithiophosphate and heated metal surfaces, coupled with an analysis of the surface product(s) formed, indicate that additives of this type owe their effectiveness to a dual mechanism. At temperatures between 200 and 600°C the...

Full description

Saved in:
Bibliographic Details
Published in:Wear 1982-04, Vol.77 (3), p.355-384
Main Authors: Barcroft, F.T., Bird, R.J., Hutton, J.F., Park, D.
Format: Article
Language:English
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:Measurements of the kinetics of interaction between a typical zinc dialkyl dithiophosphate and heated metal surfaces, coupled with an analysis of the surface product(s) formed, indicate that additives of this type owe their effectiveness to a dual mechanism. At temperatures between 200 and 600°C the thiophosphate additive forms a deposit on the surface, its composition varying regularly with temperature and having a melting point of about 950°C. Deposits of the same generic type are also formed on the surfaces of non-interactive metals such as platinum and gold. At temperatures above about 600°C the thiophosphate also reacts with ferrous metal surfaces to form films that are predominantly iron sulphide but which also contain an iron phosphide. Analysis of extreme pressure (EP) films formed in practical systems lubricated by oils containing zinc thiophosphate additives are consistent with this dual mechanism. It is possible, moreover, to gain some idea of minimum temperatures generated at the metal-metal interface in practical systems from a knowledge of the relative atomic abundance of elements in the EP layer produced by these additives.
ISSN:0043-1648
1873-2577
DOI:10.1016/0043-1648(82)90061-8